The invention relates to a device for air conditioning a motor-vehicle passenger compartment.
A device of this type, in the usual way, includes an air-conditioning loop equipped with an evaporator, with a compressor, with a condenser and with a pressure-reducing valve, which are traversed by a refrigerant fluid. A motor-driven fan unit is generally able to produce airflow for cooling the engine of the vehicle. This airflow additionally passes over the condenser in order to cool it.
In practice, the motor-driven fan unit is powered electrically via a control module in order to vary its speed and hence the airflow passing over the condenser.
The cooling power of the air-conditioning loop can thus be defined, on the one hand, by the offset between a high pressure of the refrigerant fluid at the outlet from the compressor and a low pressure of the fluid at the inlet to the compressor and, on the other hand, by the quantity of air which passes over the condenser.
A passenger in the passenger compartment, via a control element, generally sets a selected value relating to a cooling power desired in the passenger compartment. Typically, if an increase in this cooling power is wanted, there ensues an increase in the offset between the high and low pressures mentioned above and an increase in the speed of the motor-driven fan unit.
However, if the condenser is sufficiently well ventilated, especially due to a high speed of the vehicle or by a wind incident on the vehicle, it is not necessary to trigger or to increase the speed of the motor-driven fan unit.
However, in the known air-conditioning devices of the abovementioned type, a demand for an increase in the cooling power of the loop systematically entails an increase, at least in steps, of the speed of the motor-driven fan unit and of its electrical power supply. This gives rise, especially when the vehicle is driving at high speed, to an unnecessary triggering or to an inadvertent increase in the speed of the motor-driven fan unit, which entails more rapid wear on it and wastage of the electrical power supply.
The present invention aims to improve the situation.
To that end the invention proposes an air-conditioning device of the type described above, wherein means are provided for recording a parameter representative of an air throughput passing over the condenser, this air throughput comprising or not comprising an air throughput produced by the motor-driven fan unit.
According to the present invention there is provided a device for air conditioning a motor-vehicle passenger compartment, comprising an air-conditioning loop traversed by a refrigerant fluid, a compressor and a condenser, the condenser being intended to be traversed by an airflow which is produced, at least in part, by a motor-driven fan unit powered electrically via a control module, and further including: means for recording a parameter representative of an air throughput passing over the condenser, the said air throughput comprising or not comprising the air throughput produced by the motor-driven fan unit, and a regulation module, suitable for interacting with the said means and capable of estimating a maximum value for the electrical power supply to the motor-driven fan unit, for a given air throughput and for a given cooling power of the air-conditioning loop, which corresponds to a predetermined, high-pressure value of the refrigerant fluid at the outlet from the compressor, wherein the regulation module is configured to co-operate with the control module in order to limit the electrical power supply to the motor-driven fan unit substantially to the said maximum value, as a function of the air throughput and of the high-pressure value at the outlet from the compressor.
The device according to the invention comprises a regulation module, able to interact with the abovementioned means and capable, for a given air throughput, of estimating a maximum value for the electrical power supply to the motor-driven fan unit. The regulation module can then cooperate with the control module with a view to limiting the electrical power supply to the motor-driven fan unit substantially to this maximum value, as a function of the air throughput.
Thus the electrical power supply to the motor-driven fan unit is limited to a maximum value which is estimated as a function of the air throughput passing over the condenser. This air may originate, at least in part, from the flow produced by the motor-driven fan unit and/or the speed of the vehicle and/or a wind incident on the vehicle. Hence it is estimated that, depending on the speed of the vehicle and, more precisely, depending on the speed differential between the speed of the vehicle and that of the wind, it is no longer necessary to augment the air throughput passing over the condenser via an increase in the power of the motor-driven fan unit beyond a maximum value, even if an increase in the cooling power of the loop is wanted. In contrast, the value of the high pressure at the outlet from the compressor may still increase in proportion to the desired cooling power.
Nevertheless, for reasons of safety, neither should this high-pressure value go beyond a maximum value fixed by the constructors. Furthermore, the engine of the vehicle remains the priority for the choice of the operation of the motor-driven fan unit. In practice, an engine-temperature sensor is provided, linked to the control module of the motor-driven fan unit so as to trigger it and/or vary its speed. Hence, if the engine requires a triggering or an increase in the speed of the motor-driven fan unit, this triggering or this increase in speed is effective even if the power supply to the unit has reached the maximum value estimated by the module for regulating the air-conditioning device according to the invention.
Advantageously, the regulation module is connected to a vehicle speed sensor, and takes account of the speed of the vehicle in evaluating the maximum value of electrical power supply to the motor-driven fan unit.
In one, further developed, embodiment, the regulation module is connected to an anemometer sensor configured to record an airspeed of air incident on the vehicle, proportional to an air throughput passing over the condenser and not produced by the motor-driven fan unit. The regulation module then takes account of the speed of the vehicle and of a wind incident on the vehicle in order to evaluate the abovementioned maximum value of electrical power supply to the motor-driven fan unit.
According to another advantageous characteristic of the invention, the regulation module is furthermore configured to estimate the maximum value of the electrical power supply to the motor-driven fan unit, for a given cooling power of the air-conditioning loop which corresponds to a predetermined value of high pressure of the refrigerant fluid at the outlet from the compressor.
Means are advantageously provided for recording a parameter representative of a high pressure of the refrigerant fluid at the outlet from the compressor.
Particularly advantageously, the regulation module is capable moreover, for a given air throughput, of evaluating a value of electrical power supply to the motor-driven fan unit, below the abovementioned maximum value, as a function of a reduction in high pressure towards high-pressure values below the predetermined value of the high pressure. The regulation module is then configured to co-operate with the control module with a view to adjusting the electrical power supply to the motor-driven fan unit to a value in keeping with a high-pressure value below the predetermined high-pressure value.
Hence, for a given cooling power, the electrical power supply to the motor-driven fan unit is limited to a maximum value which is estimated as a function of an air throughput incident on the condenser.
The regulation module is preferably configured to evaluate the correspondence between the value of electrical power supply to the motor-driven fan unit and a high-pressure value below the predetermined high-pressure value, according to a chosen model of substantially reciprocal quadratic variation.
In one, more developed, embodiment, the device includes means for recording a parameter representative of a low pressure of the fluid at the inlet to the compressor. The regulation module is then configured to evaluate the correspondence between the power-supply value and the reduction in the high pressure, as a function of this low pressure of the fluid.
The compressor is preferably of the xe2x80x9cexternal controlxe2x80x9d type and the regulation module is connected to a sensor of the electrical power supply current to the compressor, this electric current being representative of the fluid low pressure at the inlet to the compressor.
In one variant according to which the compressor is of the xe2x80x9cinternal controlxe2x80x9d type, the regulation module is connected to a sensor of the temperature of the airflow leaving the evaporator, this temperature being representative of the fluid low pressure at the inlet to the compressor.